Archaeometric Aspects of White and Coloured Marbles Used in Antiquity: the State of the Art
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Per. Mineral. (2004), 73, 113-125 http://go.to/permin SPECIAL ISSUE 3: A showcase of the Italian research in applied petrology An International Journal of MINERALOGY, CRYSTALLOGRAPHY, GEOCHEMISTRY, ORE DEPOSITS, PETROLOGY, VOLCANOLOGY and applied topics on Environment, Archaeometry and Cultural Heritage Archaeometric aspects of white and coloured marbles used in antiquity: the state of the art LORENZO LAZZARINI* Laboratorio di Analisi dei Materiali Antichi, Dipartimento di Storia dell’Architettura, Università IUAV di Venezia, S. Polo 2468 – 30125 – Venezia. ABSTRACT. — As is well known, the identification metodologia. Attualmente le più alte probabilità di of the quarry of ancient marble artefacts is of the successo si raggiungono combinando due o più utmost interest to archaeologists and art historians. tecniche analitiche. Nell’articolo si presenta una Scholars of different disciplines have been trying for breve storia degli studi, e vengono considerate le more than a century such an identification by means tecniche e le combinazioni più usate, in particolare of a unique laboratory analysis without positive quella dell’esame petrografico di sezioni sottili e results. To-date the best probabilities of success are l’analisi degli isotopi stabili del C e dell’O che si obtained by combining together two or more avvantaggia della più completa banca dati di analytical techniques. The paper presents a short riferimento esistente per i marmi più importanti usati history of the important studies, namely those in antico. Di quest’ultimi, oltre ad alcune essenziali regarding the most frequently used combinations, informazioni circa le località di cava, i periodi di uso with particular reference to the petrographic e la bibliografia specifica più recente, si riportano i examination of a thin section and the determination diagrammi dell’MGS (Maximum Grain Size) e of the C & O stable isotopic ratios on the same isotopici più utili per la loro identificazione. sample. Such a combination takes advantage of the best existing database for the marbles most KEY WORDS: ancient white and coloured marbles, commonly used in antiquity. Of these are reported quarries, archaeometric identification, state of the the essential information on their quarries, periods of art. use and specific bibliography, together with the MGS (Maximum Grain Size) and isotopic diagrams useful for their identification. INTRODUCTION RIASSUNTO. — Come è noto, l’identificazione della cava di manufatti marmorei antichi riveste un The first scholar to take an interest in the grande interesse archeologico e storico-artistico. Da problem of identifying marbles of oltre un secolo si tenta di raggiungerla con indagini Mediterranean origin that were used in ancient di laboratorio le più varie, senza peraltro essere times, for the purposes of art history as well as giunti a risultati univoci impiegando una sola archaeology, was Winkelmann, as far back as the end of the XVIII century. His interest was * E-mail: [email protected]. taken up by whole generations of scholars but 114 L. LAZZARINI it was not until a hundred years later that R. area of production; monuments (latu sensu) that Lepsius (Lepsius, 1890) developed the first are properly dated can in turn tell us when scientifically correct approach, one that can certain quarries were being worked and hence unreservedly be defined as archaeometric in the the demand for the marbles concerned; the strict modern sense of the term. identification of marbles forming part of sunken What follows is a rapid historical overview cargoes enables ancient trade routes to be of archaeometric studies applied to true reconstructed; location of the quarry from which marbles, white, grey and coloured, dwelling a damaged marble came makes it possible to more on the methods currently most frequently find sound material for the purpose of used to solve the «problem of the provenance» restorations, replacements, copies, etc.. of marble artefacts and focusing in particular So far the many studies that have set out to on the methodology followed by the author in determine the provenance of marbles used in the study of many ancient marble monuments antiquity have led to results which are partial and objects, including those at Ostia, examined and not always satisfactory from a scientific in the framework of what is certainly the most point of view, especially when identification extensive archaeometric survey so far to have was based on macroscopic examination, on been undertaken. visual evidence such as the colour, brilliance or Marbles in the proper sense of the word, that grain of the stone. Such identifications almost is pure carbonatic (calcitic and/or dolomitic) always turn out to be wrong (Renfrew and rocks with a carbonate content that is usually Springer Peacy, 1968), essentially because it is well in excess of 95% – they are crystalline, often found that samples of marble from the they may be white or grey or red or green and same quarry have different autoptic properties they will have been produced by contact or while others from different quarries, sometimes regional metamorphism – are quite common a long way from each other, are identical. throughout the Mediterranean area. Many of More reliable are identifications based on the them were used in antiquity, both in pre- and mineralogical and petrographic study of thin early-historical periods (late Neolithic – sections (Herz and Pritchett 1953, Herz 1955, Cycladic civilizations) and also in the Greek Weiss 1954, Renfrew and Springer Peacy and Roman and later times, when the quantity 1968, Young and Ashmole 1968); some of of marble employed and the quality of the these are often difficult and time-consuming to workmanship often reached remarkable levels. perform however (e.g. petrotectonic In the case of some marbles we know when examinations), and they cannot always cope they were used for the first time and we have with the sometimes considerable local information from various sources that enables variability in mineralogical (e.g. with the us to build up at least a partial picture of their contents of dolomite) and petrographic (e.g. distribution and how they were traded and granulometric) characteristics of pure marbles, transported. In most cases however, we really even though pure marbles are among the most know very little, mainly because of the homogeneous mono-mineralic rocks known. fundamental difficulty of identifying marbles Better results have been achieved by reliably when they are found as original geochemical studies of the trace elements structural or decorative elements of ancient present in marble samples taken from ancient buildings or in sculptures, or when they are re- quarries. For example, certain Anatolian used in Mediaeval or Renaissance monuments marbles can be distinguished from their Attic (e.g. in Rome and Venice). counterparts on the basis of sodium and It is of great importance to archaeologists that manganese content (Rybach and Nissen 1964), the identification of marbles should be based on but this criterion cannot be used to discriminate scientific data: sculptures of uncertain attribution between Attic marbles and those from the can be ascribed to a specific artist or «atelier» or Cyclades. Archaeometric aspects of white and coloured marbles used in antiquity: the state of the art 115 Another problem is that in the case of both Another early pluridisciplinary contribution Na and Mn there are often considerable involving a combination of petrographic quantitative variations in different samples characteristics (average grain size, type of from the same quarry or in different parts of a crystal shape and structure, semi-quantitative single sample. This can be explained by the assessment of accessory minerals) and the presence of concentrations of these elements in determination of the Calcium/Strontium ratio minerals other than calcite, e.g. epidotes and was proposed by Lazzarini et al. in 1980 micas, the distribution of which in the structure (1980a). This geochemical ratio was of the marble may be quite casual. This makes considered especially important in pure the identification of marble considerably more marbles for various reasons. Strontium is an difficult in cases where just one small sample is isomorphous element of calcium, which it can available. A more recent study (L. Conforto et replace by up to 4% in aragonite (this al. 1975), which examined only marbles of strontium-rich aragonite has been given the Anatolian and Italian origin and determined name mossotite), while it rarely exceeds 1% in their contents in terms of eight trace elements calcite (Chilingar et al. 1967). Most of the (K, Fe, Mn, Si, Ba, Al, Sr and Ti), has given marbles in this study are the product of the partial results, similar to those of the preceding metamorphism of organogenic limestones or in technique, and has thus enabled us to any case contain the remains of fossil characterize certain quarries with respect to organisms, as was also shown by petrographic others. studies of the marbles of Attica (Marinos, But ultimately, the limits of a method of 1948) and the island of Lesbos (Lazzarini et identification that is based on the determination al., 1999). Now, the protective shell or skeleton of oligo-elements lie in the fact that their of many organisms is made of aragonite, the interval of variation is frequently the same for preference for this polymorphous form of samples from different petrographic regions. CaCO3 rather than calcite being regulated by The approach based on measurement of the temperature. Temperature also controls the isotopic ratios of carbon and oxygen has looked Ca/Sr ratio, which remains unaltered in marbles interesting and promising ever since its first (metamorphism being an essentially appearance: it enabled Craig and Craig (1972) isochemical process) so this datum can be to distinguish Greek marbles from Attica from useful in estimating the thermic level reached their counterparts in the Cyclades and L. by these rocks. Soviet scholars (Vinogradov et Manfra et al. (1975) to distinguish between al., 1952) showed that the Ca/Sr ratio is higher marble from various localities in Asia Minor.